For an exhaust gas of a diesel engine, reduction of nitrogen oxides (NOx) and soot is one of the most important problems. Introduction of EGR gas is effective as a countermeasure for NOx in a medium load operation (acceleration), but the fresh air decreases and the soot increases in normal EGR. As a conventional technique capable of solving this problem, there is one using an exhaust blowdown pressure near the bottom dead center of an expansion stroke of one cylinder to supercharge EGR gas into another cylinder which is different from the one cylinder in combustion timing (see Patent Document 1), or one using an exhaust pressure by an exhaust throttle to supercharge the EGR gas (see Non-patent Document 1).    [Patent Document 1] Japanese Patent Publication No. S51-34526    [Non-patent Document 1] ASME80-DGP-8